The invention relates to a lancet device for a face-to-face weaving machine and furthermore to a face-to-face weaving machine provided with such a device.
When weaving face-to-face, two pile fabrics are woven at the same time. An upper and a lower backing fabric consisting of warp yarns and weft yarns, while pile warp yarns are interlaced in both backing fabric alternately. The parts of the pile warp yarns running between the two backing fabrics are cut through afterwards. In this manner, on each backing fabric a series of little ends of pile yarn standing upright are obtained. It is very important for the quality of the pile fabrics that the pile height all along the fabric is as constant as possible. As the intermediate distance between the upper and the lower fabric is determinant for the length of the parts of the pile warp yarns running between the two fabrics and therefore also for the pile height, this intermediate distance should be kept as constant as possible when weaving face-to-face. In order to obtain this, use is made of lancet devices on face-to-face weaving machines with two weft insertion levels. In doing so, a series of lancets is placed in a lancet holder evenly spread over the weft width and extending in the warp direction between the warp yarn systems and between the blades of the weaving reed. These lancets serve as spacers in order to keep the two backing fabrics at an intermediate distance from one another.
Known lancet devices for face-to-face weaving machines having two weft insertion levels are comprising lancets consisting of an elongated metal strip of a restricted thickness (for instance, 0.1, 0.2, 0.3 or 0.4 mm) and with a height being equal to the intermediate distance desired between the two backing fabrics in face-to-face weaving, for instance 3, 5, 8, 10, 15, 18, 20, 22, 24, 30 mm. One extremity is provided to be received by the lancet holder, while the other extremity is ending in a point, the point being situated above the lower cutting table of the weaving machine. The pointed tip may be made so as to be stepped symmetrically. When the so-called stepped lancets are shifted in the warp direction the lancet will take up another height near the reed and so it is possible to realize various pile heights with the same lancet device (and so the same lancet device enables us to realize different heights). When using such stepped lancets, the lancet height corresponds with the height of the topmost step. When high lancets are used, the various shed forming elements have to shift the warp yarns over greater heights, irrespective of the lancet height that has been adjusted or, in other words, irrespective of the pile height that has been adjusted. This is at the expense of weaving speed and weaving efficiency.
Other applications are known with greater lancet heights, for instance up to 70 and 90 mm in the form of spoon lancets, as represented in FIG. 10, where only at top level the full width is used and thereafter a smaller width is chosen in order to reduce the distance between the 2 rapiers to reduce the shed to be made.
Sometimes lancets with the usual heights up to 30 mm are also locally carried out with a constriction heightwise in order to draw the rapiers nearer to one another and to reduce the shed.
In weaving face-to-face fabrics, there is a distinct tendency to realize higher densities (a reed density of 500 or densities corresponding to a reed density of 700 or more) in combination with more colors. This leads to an increase of the number of warp yarns per meter of weaving width and the available space for the warp yarns to cross is restricted. These problems are still compounded by the presence of elements like healds with heald eyes (both for backing warp yarns and pile warp yarns), blades for the weaving reed and lancets as spacers. The same problems apply with lower densities when using thicker yarns.
To make crossing of the warp yarns (backing and pile warp yarns) less troublesome, various solutions are known.
It is known to take duplex healds as healds for the backing warp yarns, in order to solve the problem that the heald eyes may be getting so close together at high densities of the warp yarns, that a crossing of the remaining backing warp yarns and pile warp yarns may lead to friction, damage, fraying, rupture or getting stuck of these yarns. The healds being provided in two embodiments, being used alternately next to one another in a weaving frame, and the heald eyes of the first healds being situated in a row, in weaving direction after the row that is constituted by the second row of heald eyes. In this manner, more space is available near the healds of the backing warp yarns for the pile and backing warp yarns to be crossed, by dividing the healds into 2 levels situated one behind the other.
In U.S. Pat. No. 6,176,270 such a solution is described, essentially in view of using thick warp yarns for weaving and where, moreover, the healds near the receiving eyes are made elastic in order to be more resistant to dynamic charges.
According to patent EP 651 083 it is also known to provide the blades of a weaving reed with a recess, the back part being shifted parallel and laterally in the weft direction with respect to the front part. According to the description of the invention, this will enable the back part to be used as a deflector heald and to prevent pile warp yarns of the same pile warp yarn system from getting tangled or to separate the backing warp yarns and the pile warp yarns within a same warp yarn system. However, such a weaving reed is in practice also used as a double reed, a complete warp yarn system being inserted between each front and adjacent back part of a reed dent. Because of the foremost and the back reed dent parts being shifted with respect to one another, the warp yarns have more space within a pile warp yarn system to find their way to the face-to-face fabric.
Furthermore, in EP 1 347 086, a solution is proposed near the weaving reed, where per physical reed dent, two pile warp yarn systems and two (partially) backing warp systems have been provided. This method also enables us to produce more space for the pile warp yarns near the weaving reed in order to find their way to the face-to-face fabric.
However, none of these solutions is offering a solution for face-to-face weaving with lancets in the zone of the harness where in each warp yarn system a lancet is extending and the heald eyes of the pile warp yarns have to move between the lancets where there are already a number of pile warp yarns and healds for pile warp yarns. In face-to-face weaving on double rapier weaving machines it often happens that at each pick almost half of the dead pile is in the center, which means that the corresponding heald eyes are possibly situated between the lancets. This will strongly restrict the space for the pile warp yarns for crossing. This leads to an accelerated wear of the healds. In order to render the weaving process somewhat feasible and reliable, the spring tension is increased in order to have more force to pass a heald with pile warp yarn through this bundle.
It is known, in weaving with higher densities of warp yarns, to insert a lancet in one reed dent and no lancet in the next reed dent alternately. However, this has the disadvantage that in the reed tooth with the lancet, the weft is well kept at a distance, whereas in the next reed dent without a lancet, the weft is drawn nearer the center because of the tension of the pile warp yarns, so that the fabric will show an unwanted ribbed aspect. This aspect is very pronounced with the 1/1 V-weave, where part of the pile forming pile warp yarns is pulling at the binding warp and because of which the pile burl has itself interlaced at another height than the next pile burl adjacent in the weft direction, being kept at a distance by a lancet and also at another height than the pile burl before or after in the warp direction being interlaced on a tension warp yarn.